1. Field of the Invention
The present invention relates to a hand-held gardening machine such as a hedge trimmer. In particular, a hand-held gardening machine comprising a pair of upper and lower clipper blades which are caused to reciprocate.
2. Description of the Prior Art
In general, a hand-held gardening machine of this type uses output from a power source such as an internal combustion engine or an electric motor to cause a pair of upper and lower elongate clipper blades to reciprocate relative to each other in a longitudinal direction thereof.
In recent years, various safety standards as safety measures have been tending to be established in many countries in view of increasing accidents caused in working such as trimming operation. For example, a trimmer comprising clipper blades falls under such safety standards, because an operator is exposed to a possible danger, in particular, a serious accident due to contact between the clipper blade(s) and operator's leg or the like during operation. To meet such requirements, a comb-like safety plate is mounted above or below the upper and lower blades supported slidably each other. FIG. 8 shows a clipper blade working portion of such a hand-held gardening machine.
In FIG. 8, clipper blades 40, 50 which are laid one on top of the other are held, for example, between a comb-like safety plate 60 having protrusions 61, 61, . . . which is located below the bottom surface of the lower clipper blade 50 and a supporting plate 70 which is located above the top surface of the upper clipper blade 40, and supported slidably to-and-fro by means of mounting means 71 such as a screw.
The protrusions 61, 61, . . . are so formed that tips thereof protrude beyond tips of the teeth 41, 41, . . . and 51, 51, . . . by d.sub.1 (for example, 8 mm or more). It is prescribed in the safety standard (UL standard) that when operator's leg M of a diameter assumed to be, for example, 120 mm is brought in contact with the protrusions 61, 61 of the safety plate 60 which are adjacent to each other, the distance between the tip of the tooth 41 or 51 and the portion of the leg M which is closest thereto is d.sub.2 (for example, 4 mm or more), in terms of safety measures.
As seen from FIG. 8, each of the pitches between neighboring teeth 41 and 41 and between neighboring teeth 51 and 51 of the upper and lower clipper blades 40, 50 and the pitch between neighboring protrusions 61 and 61 of the safety plate 60 are formed to be equal.
As shown in FIG. 8 by the solid line, the teeth 41, 41, . . . and 51, 51, . . . are so mounted as to overlap each other at their starting points of stroke (hereinafter referred to as a first dead center). In the following description, explanation will be given only on neighboring two teeth 41, 51, and protrusions 61, 61 as a matter of convenience. Needless to say, however, the same operation is true of other counterparts.
The upper and lower blades 40, 50 are respectively formed with elongate holes 42, 52 which allow relative movement thereof with respect to the screw 71 (the supporting plate 70) so that the teeth 41, 51 initiate reciprocating motion from the first dead center as a starting point and overlap again at the position shown in FIG. 8 by the chain-double dotted line (hereinafter referred to as a second dead center) to terminate forward stroke. The longitudinal length of each of the elongate holes 42, 52 is equal to stroke S (travel) of each of the teeth 41, 51, and this is equal to the distance between the first dead center and the second dead center.
The protrusion 61 of the safety plate 60 is so fixedly mounted by means of the screw 71 as to overlap the overlapping position of the teeth 41, 51 at their first dead centers.
By this structure, the upper tooth 41 at position II and the lower tooth 51 at position I when present at their first dead centers are adapted to overlap together at position III when present at their second dead centers and then return to the original positions at the end of return stroke. In this connection, the relationship between the positions I, II, III and the stroke S is as shown in FIG. 3. Thus, the upper and lower teeth 41, 51 is adapted to cut a plant A or the like in the course of the forward stroke from the first dead center to the second dead center.
In such a conventional hand-held gardening machine as described above, however, a plant or the like having a small diameter is likely to be caught in the gap between the tooth 41 or 51 and the protrusion 61 during the return stroke of the tooth 41 or 51 from the second dead center to the first dead center. Inconveniently, as described later in detail, it is difficult to cut the thus caught plant completely because no edge is formed on either side of the protrusion 61 of the safety plate 60. In such a condition that the slender branch or the like is involved as a foreign obstacle in the gap between the tooth 41 or 51 and the protrusion 61, there is a problem that the upper and lower clipper blades 40, 50 are prevented from smoothly reciprocating to result not only in lowered operational efficiency but also in increased power loss.